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A protein such as C-reactive protein or mannose-binding protein that is related to the development of the inflammatory response but is seen only in acutely ill patients.

Acute phase protein

A specific host defense composed of the humoral (antibody) and cellular immune responses. It has memory and takes several days to get started.

Adaptive immune response

Leukocytes (monocytes or lymphocytes) that lack granules in the cytoplasm.


One of the sequences of reactions seen in the complement system of innate immune response initiated by factors B, D, or P.

Alternative pathway of complement activation

A macrophage that is found in the alveoli of the lungs.

Alveolar macrophage

Development of blood vessels.


Proteins produced through stimulation by interferon that become active in the presence of double-stranded RNA and can protect cells from being infected with virus.

Antiviral proteins

Genetically programmed cell death; a process in which the cell commits a kind of suicide. This occurs when cells are worn out or if specific signals are given to the cell, as in cytotoxic reactions.


A type of white blood cell containing large numbers of granules. This cell releases histamine and other molecules as part of the inflammatory response.


An acute-phase protein that binds to phospholipids and is seen in acute infections.

C-reactive protein (CRP)

A laboratory procedure in which the formed elements (cells) of the blood are counted. This information can be of great value in determining the stage of infection seen in a patient.

CBC (complete blood count)

A nonrandom movement of an organism toward or away from a chemical.


A group of cell-surface proteins that are essential to immune recognition reactions. Class I MHC molecules are involved in natural killing functions and are found on all cells except those involved in the adaptive immune response.

Class I MHC

A group of proteins found only on the surface of cells, involved in the adaptive immune response. These proteins are absent until an immune response is generated and they have an important role in antigen presentation.

Class II MHC

One of the ways in which the innate immune response works to protect the body. This pathway responds to antigens that have been seen previously and involves antibody against those antigens.

Classical pathway of complement

A set of more than 20 proteins found in the blood that when activated can destroy bacteria by making holes in the bacterial cell wall. This system also amplifies the inflammatory response to infection.

Complement system

A phagocytic cell found in the dermis; responsible for antigen presentation to helper T cells in the adaptive immune response.

Dendritic cell

The process in which white blood cells make their way to the site of infection. It includes margination, in which cells adhere to vessel walls, and emigration, in which cells leave the blood vessels.


A routine lab test in which the percentage of each of the white blood cell populations is determined.

Differential blood analysis

A white blood cell normally found in very low numbers in the blood but in very high numbers during a parasitic infection.


Chemical molecules found in the blood that respond to carbohydrates found on bacteria and initiate the alternative pathway of complement.

Factors B, D, and P (properdin)

A body temperature that is abnormally high.


A substance that recruits large numbers of phagocytic cells to the site of infection.

Granulocyte-macrophage colony-stimulating factor

A leukocyte (white blood cell) with granular cytoplasm and an irregularly shaped nucleus.


A protease enzyme secreted by killer cells that causes the death of a target cell by triggering apoptosis.


Condition resulting from reduced levels of oxygen being supplied to the tissues.


The body's defensive response to any trauma or infection of the body.


The nonspecific immune response that is present at birth.

Innate immune response

A group of small protein molecules often released in response to a viral infection that bind to noninfected cells, causing them to produce antiviral proteins that protect against viral infection of the cell.


The best-known endogenous pyrogen, which causes the onset of fever during an infection.

Interleukin 1 (IL-1)

A cytokine produced during an infection that causes the liver to produce acute-phase proteins.

Interleukin 6 (IL-6)

Cells found in the stroma of the lung. They are smaller and less phagocytic than alveolar macrophages.

Interstitial macrophages

A phagocytic cell that is stationed in the sinusoids of the liver.

Kupffer cell

The structures associated with the production and recycling of tears.

Lacrimal apparatus

The gland that produces tears. It is part of the lacrimal apparatus.

Lacrimal gland

Dendritic cells found in the layers of the skin. They are phagocytes that are one type of antigen-presenting cell.

Langerhans cells

The complement pathway that is activated by the carbohydrate mannose.

Lectin-binding pathway

A factor that lowers plasma iron concentration, which limits the availability of iron and thereby inhibits the growth of some pathogens.

Leukocyte endogenous mediator

A white blood cell.


A chemical substance released from mast cells that causes prolonged airway constriction, increased dilation and permeability of capillaries, increased secretion of mucus, and stimulation of nerve endings that causes pain and itching.


A substance that inhibits the scavenging of iron by pathogens, thereby inhibiting their growth.


A form of white blood cell that is involved with the adaptive immune response of the body.


An antibacterial enzyme found in secretions such as tears and saliva.


Specialized cells found in the digestive tract. They are used by pathogens to enter the tissues of the body.

M cells

A highly phagocytic white blood cell.


Acute-phase protein that binds to mannose sugars found on many bacterial and fungal cell membranes.

Mannose-binding protein (MBP)

The process in which white blood cells traveling in the blood are able to slow down and stop adjacent to the area where the tissue injury has occurred. It is caused by the localized secretion of selectin, which is a sticky molecule on the inner side of the vessels.


A white blood cell that releases histamines during an allergic response.

Mast cell

The complex formed during the final stages of the complement pathway. This complex produces a hole in the cell wall of bacteria, leading to their death.

Membrane attack complex (MAC)

Resident macrophages found in the central nervous system. There are two forms, ameboid (which travel through developing brain tissue and are also found in damaged brain tissue) and ramified (found in normal brain tissue).

Microglial cells

A nonphagocytic white blood cell found in the blood that will differentiate into a phagocytic macrophage in response to an infection.


Formerly called the reticuloendothelial system. It is a collection of phagocytic cells and tissues that contain phagocytic cells, located throughout the body.

Mononuclear phagocytic system

Mechanism involving ciliated cells that allows materials in the bronchi, trapped in mucus, to be lifted up into the pharynx and subsequently swallowed or spat out.

Mucociliary escalator

Large granular cells found in the peripheral tissue and blood that kill tumor cells, virus-infected cells, bacteria, fungi, and parasites.

Natural killer cells

A phagocytic white blood cell.


An enzyme released by cytotoxic cells that leads to the destruction of target cells.


A cell that can carry out phagocytosis.


Ingestion of materials into cells by means of vacuole formation.


A structure resulting from the fusion of a phagosome with a lysosome.


A vacuole that forms around an organism within the phagocyte that engulfed it.


Another name for a neutrophil (a phagocytic white blood cell).

Polymorphonuclear leukocyte

The alternative complement pathway that is activated by contact between lipopolysaccharides and endotoxins on the surface of pathogens and three factors found in the blood (factor B, factor D, and factor P).

Properdin pathway

Chemical mediators that act as cell regulators and are produced during the inflammatory response. They can stimulate pain and fever responses.


Chemicals that can induce a fever response.


Phagocytic cells that are stationed in specific tissues throughout the body.

Resident (fixed) macrophages

The exocytotic vesicle containing the elements of the destroyed organism. It is seen at the end of the phagocytic process.

Residual body

Structural fibers made of collagen that form a meshwork supporting soft tissue.

Reticular fibers

Old term for what is now known as the mononuclear phagocytic system.

Reticuloendothelial system

Oily substance secreted by the sebaceous glands.


A molecule that is secreted from the epithelial cells of blood vessels that causes the margination of white blood cells at the site of the tissue damage.


Also known as tumor necrosis factor. A chemical cytokine seen in the inflammatory and immune response to infection.


Molecules located on the surface of cells that defend the body. These receptors bind to antigens found on pathogens.

Toll-like receptors

A substance that binds iron.


A chemical cytokine seen in the inflammatory and immune response to infection.

Tumor necrosis factor (TNF)

Phagocytic cells that circulate in the blood or move into tissues when microbes or other foreign materials are present.

Wandering macrophages

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